Answer: The right answer is the A) "... banked with dirt to a height of..."
Explanation: Just to elaborate a little on the answer, it can be added that this is the choice with the most grammatically correct structure. Options D and E should be discarded, primarily because they unnecessarily repeat the verb "was." In addition, option C can also be discarded, since the pronoun "them" is incorrectly used—the verb "banked" is referring to the framework of poles, and this is singular. Finally, option B should also be discarded, since the phrase would require the use of a comparative element—"as that of a three feet high table," for instance.